1. Field of the Invention
The present invention relates to a semiconductor device such as a data line driver of a liquid crystal display (LCD) apparatus, and more particularly, to the improvement of generation of a bias changing signal for changing a bias current flowing through an operational amplifier (voltage follower) for driving a capacitive load.
2. Description of the Related Art
In a prior art semiconductor device such as a prior art data line driver of an LCD apparatus, a plurality of voltage followers are provided to drive a plurality of capacitive loads such data lines in accordance with a control signal such as a strobe signal. Also, a bias circuit controls bias currents flowing through the voltage followers in accordance with an externally-generated bias changing signal. That is, in a high access mode state, the bias currents are increased to increase the operation speed while the power consumption is increased. On the other hand, in a low access mode, the bias currents are decreased to decrease the operation speed while the power consumption is decreased. This will be explained later in detail.
In the above-described prior art semiconductor device, however, the bias changing signal in synchronization with the control signal has to be input as an external signal to the bias circuit, which is a burden on the user. Additionally, when the number of capacitive loads is increased, or when the resistance and capacity of the LCD panel fluctuates due to the manufacturing process thereof, the bias changing signal has to be adjusted by the user, which is another burden on the user.